Completely Unable to Define the UpdateCallback of System.Runtime.Caching

Question

I'm having a difficult time using the CacheEntryUpdateCallback delegate of the System.Runtime.Caching library. Whenever I define and set the callback, I get an ArgumentException that the "CacheItemUpdateCallback must be null". Why must it be null? I should be able to set this and then get the callback.

I do not get this when using the CacheEntryRemovedCallback delegate. I can reliably reproduce this in all of my projects. Am I doing something wrong? Here's a small sample application:

using System.Runtime.Caching;
class Program {
  static void Main(string[] args) {
    var policy = new CacheItemPolicy();
    policy.SlidingExpiration = TimeSpan.FromSeconds(10);

    // this works
    //policy.RemovedCallback = Removed;

    // this creates the exception
    policy.UpdateCallback = Update;

    MemoryCache.Default.Add("test", "123", policy);
    Console.Read();
  }

  static void Update(CacheEntryUpdateArguments arguments) { }
  static void Removed(CacheEntryRemovedArugments arguments) { }
}

Answer 1

According to documentation you should be using Set instead of Add.

MemoryCache.Add:

The Add and AddOrGetExisting method overloads do not support the UpdateCallback property. Therefore, to set the UpdateCallback property for a cache entry, use the Set method overloads instead.

Following indeed work without problems:

MemoryCache.Default.Set("test", "123", policy);